This application relates to a control logic for maintaining proper solution concentration within an absorption chiller, and to add safeguards in system control which will insure robust operation when operated in co-generation applications with heat sources like micro-turbines, reciprocating engines, etc. Improper management of the heat flowing into the chiller from theses sources can result in crystallization of the absorption solution, which is undesirable
Refrigerant absorption cycles have been used for decades to provide a cooled or heated water source for environmental temperature control in buildings. As is known, an absorber and an evaporator in a refrigerant absorption cycle selectively receive a concentrated absorption fluid, such as a LiBr solution, and a separate refrigerant (often water), respectively. The absorption fluid selectively dropped onto separate tube sets in the absorber absorbs the refrigerant vapor generated from the evaporator. A dilute solution, containing both the absorption fluid and the refrigerant is then returned to a generator for generating a heated, concentrated absorption fluid. In the generator, a driving heat source drives the refrigerant vapor out of the mixed fluid. From the generator, the absorption fluid and removed refrigerant vapor are separately returned to the absorber and the evaporator, respectively.
The above is an over-simplification of a complex system. However, for purposes of this application, the detail of the system may be as known. Further, while the above-described system provides chilled water, absorption cycles are also utilized to provide heated water for heating of a building. This invention would extend to such systems. For purposes of this application, an absorption chiller and an absorption heater are to be defined generically in the claims as an “absorption solution/refrigerant system.” A worker of ordinary skill in the art would recognize the parallel absorption heater systems and how such systems differ from the disclosed chiller system.
A potential problem occurs with absorption chillers if an undesirable amount of heat is allowed to flow into the generator when the chiller is not operating. Generally, if the absorption fluid is not flowing from the generator, as driven by pumps, etc., heat may continue to build in the generator. This rise in heat, without fluid circulation, can cause too much liquid refrigerant being boiled from the absorption solution, resulting in absorption solution crystallization. Essentially, the liquid is boiled out of the solution leaving only the crystallized absorption material (LiBr).
One condition where this un-commanded heat flow into the generator could occur is when the chiller is in standby mode or is shut down. In some conditions, heat may still be delivered into the system due to faulty valve position, or other problems. The absorption solution is no longer being driven from the generator, heat is flowing in and the solution temperature begins to rise, raising the possibility of absorption solution crystallization.
One other problem that could occur would be an electric power failure. An absorption chiller includes a number of pumps for moving the various fluids. At power failure, all of these pumps would stop with traditional wiring and controls. The delivery of heat into the system may or may not stop dependent upon whether the heat is from a turbine, or a furnace, or whether the heat is from a device electrically powered. However, under such conditions, at a minimum even if heat is not flowing into the generator, the solution is still left in the generator once the power fails. This solution thus includes an undesirably high amount of stored thermal energy, which could result in absorption solution crystallization. As an example, at shutdown of an absorption chiller, the fluid continues to be circulated by the pumps for a period of time such that the heat is removed. When the absorption chiller is “shut down” at a power failure, this circulation will not occur, and the normal cool down will not occur, leaving an undesirably hot absorption solution in the generator which boils off refrigerant.